qapi: Drop tests for inline nested structs

A future patch will be using a 'name':{dictionary} entry in the
QAPI schema to specify a default value for an optional argument;
but existing use of inline nested structs conflicts with that goal.

More precisely, a definition in the QAPI schema associates a name
with a set of properties:

Example 1: { 'struct': 'Foo', 'data': { MEMBERS... } }
associates the global name 'Foo' with properties (meta-type struct)
and MEMBERS...

Example 2: 'mumble': TYPE
within MEMBERS... above associates 'mumble' with properties (type
TYPE) and (optional false) within type Foo

The syntax of example 1 is extensible; if we need another property,
we add another name/value pair to the dictionary (such as
'base':TYPE).  The syntax of example 2 is not extensible, because
the right hand side can only be a type.

We have used name encoding to add a property: "'*mumble': 'int'"
associates 'mumble' with (type int) and (optional true).  Nice,
but doesn't scale.  So the solution is to change our existing uses
to be syntactic sugar to an extensible form:

   NAME: TYPE   --> NAME:  { 'type': TYPE, 'optional': false }
   *ONAME: TYPE --> ONAME: { 'type': TYPE, 'optional': true }

This patch fixes the testsuite to avoid inline nested types, by
breaking the nesting into explicit types; it means that the type
is now boxed instead of unboxed in C code, but makes no difference
on the wire (and if desired, a later patch could change the
generator to not do so much boxing in C).  When touching code to
add new allocations, also convert existing allocations to
consistently prefer typesafe g_new0 over g_malloc0 when a type
name is involved.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>